Not applicable.
Not applicable.
1. Field of the Invention
The invention relates to radiography, and more particularly to radiography systems which combine aspects of both transmission and backscatter radiography, and methods thereof.
2. Background
In many industrial, military, security or medical applications, images of the internal structure of objects is required. Radiography is often used for imaging. Radiography generally comprises either conventional transmission radiography or backscatter radiography.
FIG. 1 is a schematic illustrating the configuration used for conventional transmission radiography. In conventional radiography, an image is formed by transmitting radiation from a radiation generator 105 through an internal detail 110 within object 130. Attenuated radiation is received by a radiation detector 115 which is disposed on the side of the object opposite to that of the radiation generator 105. In the case of tomography, the object 130 is generally rotated about axis perpendicular to the plane of the figure.
FIG. 2 is a schematic illustrating the configuration used for backscatter radiography. Unlike conventional radiography which relies on transmission, in backscatter radiography radiation is scattered by internal detail 210 within object 230. In backscatter radiography, the radiation generator 205 and radiation detector 215 are on the same side of the object 230. All backscatter radiography techniques allow one-sided imaging of the object since the radiation generator 205 and the radiation detector 215 arc located on the same side of the object 230. This is the same imaging configuration that people and animals use for optical viewing of the surroundings. Because of the absence of a refraction process for the penetrating radiation in backscatter radiography, image-gathering lenses cannot be used.
In backscatter radiography, illumination of an entire region of the object to be interrogated in a single snapshot has generally only been possible using a pinhole, coded aperture, or a restriction positioned between the object and the radiation detector. This generally results in either extremely inefficient sensing of the radiation, or the introduction of substantial image-obscuring structured noise, thus requiring large exposure times for typical radiation sources. An alternative includes use of a scanning pencil or fan beam for illuminating a temporal sequence of points or lines on the object surface. This also yields long exposure times and decoding algorithms having long calculation times, besides requiring an expensive scanning apparatus.
The equivalent of an optical snapshot camera capable of implementation using relatively inexpensive components which would provide high image resolution and a short exposure time would be desirable for applications which require one-sided imaging of the internal structure of objects.
A snapshot backscatter radiography (SBR) system and related method includes at least one penetrating radiation source and at least one radiation detector. The radiation detector is interposed between the object to be interrogated and the radiation source. The radiation detector transmits a portion of radiation received from the radiation source to the object. The object backscatters at least a portion of the radiation it receives, with a portion of the scattered radiation being detected by the detector.
Generally, reference (base) radiation data is obtained by using the system without the object present in a low backscatter environment. The base data is then preferably stored prior to interrogating the object. The base data can then be subtracted from the total radiation data measured by the detector which includes information from both the detector structure and spatial variation of the radiation source field, as well as the object structure. This permits generation of an image of the object. The system can interrogate a wide variety of objects or volumes, such as buried or otherwise unobservable volumes suspected of containing a bomb (e.g. landmine), luggage or cargo, or integrated circuits.
The penetrating radiation source can comprise an x-ray, gamma ray, neutron or an electron beam source. The detector can comprise a photostimuable phosphorous-based image plate or an amorphous silicon panel. The detector can also include a digitizing field screen. The system preferably includes a computer for receiving radiation data from the detector and for performing data and image processing
A radiation source controller is also preferably provided. The radiation source controller can permit the system to produce 3 dimensional (3-D) radiation data which permits the generation of a 3-D image of the object. For example, the radiation source controller can direct the radiation source to provide multiple bursts at varying radiation energy or temporal variation of a radiation energy spectrum.
The system can also include one or more collimating sheets disposed between the object and the detector. Collimating sheet(s) can be used to improve resolution or help isolate a lateral migration component of the backscattered radiation.
A snapshot backscatter radiography (SBR) based land mine detection system includes at least one penetrating radiation source and at least one radiation detector, wherein the radiation detector is interposed between a volume of earth to be interrogated and the radiation source. The radiation detector transmits a portion of incident radiation from the radiation source to an object buried in the volume of earth, wherein a portion of radiation scattered by the object is detected by the detector. The radiation source preferably comprises an x-ray source. The radiography system can include a vehicle to add mobility to the system.
The invention can also be used for luggage or cargo screening, or as an integrated circuit inspection tool. In the case of the integrated circuit inspection tool the detector can comprise a CCD array detector. In a preferred embodiment the penetrating radiation source provides selectable radiation energy. This permits generation of a 3-D image of the object interrogated to obtained without physically scanning the system or the object by compiling radiation data at a plurality of radiation energies.
A snapshot backscatter radiography (SBR) method for imaging an object includes the steps of directing penetrating forward radiation through a detector to an object to be interrogated, the detector transmitting a portion of the penetrating radiation to the object, wherein the object backscatters radiation toward the detector. By processing the radiation data collected by the detector an image of the object can be generated. When at least one collimating sheet is disposed between the object and the detector, the method can include the step of collimating the forward radiation and/or the backscattered radiation. A deconvolving image enhancement technique can in addition be applied to reduce image blurring.